In this specification, an image forming apparatus is an apparatus which forms an image on recording medium. Some examples of an image forming apparatus are an electrophotographic copying machine, an electrophotographic printer (laser printer, LED printer, etc.) and the like.
Recording medium is medium across which an image is formed with the use of an electrophotographic image formation process. Some examples of recording medium are recording paper, OHP sheet, label, and the like.
A process cartridge is a cartridge in which an electrophotographic photosensitive component, and means for processing the electrophotographic photosensitive component, are disposed together, and which is removably installable in the main assembly of an image forming apparatus.
In the field of an image forming apparatus which employs an electrophotographic image formation process, it is a common practice to employ a process cartridge system, which integrally places an electrophotographic photosensitive component (which hereafter may be referred to simply as photosensitive drum), and means for processing the photosensitive component, in a cartridge which is removably installable in the main assembly of the image forming apparatus.
A process cartridge system enables a user of an image forming apparatus to maintain the apparatus by himself or herself, that is, without relying on a service person. Thus, it can drastically improve an electrophotographic image forming apparatus in terms of maintenance. Therefore, it is widely in use in the field of an electrophotographic image forming apparatus.
A conventional process cartridge is made up of a photosensitive drum unit and a development unit. The photosensitive drum unit has a cleaning unit frame by which the photosensitive drum is held. The development unit has: a development roller as a means for developing the latent image on the photosensitive drum; a development blade; and toner as developer.
There have been known image forming apparatuses of the so-called inline type. An ordinary image forming apparatus of the inline type employs process cartridges, which correspond to four primary colors, more specifically, yellow, magenta, and cyan and black, of which a full-color image is to be synthetically formed. Each cartridge has a photosensitive drum, and a development unit. Thus, an ordinary image forming apparatus of the inline type forms a full-color image by layering yellow, magenta, cyan and black monochromatic images.
During an image forming operation, a development roller is kept pressed toward the photosensitive drum. In the case of an image forming apparatus which employs a development method which places a development roller in contact with a photosensitive drum to develop the latent image on the photosensitive drum, the development roller is kept pressed upon the peripheral surface of the photosensitive drum.
Thus, if an image forming apparatus which employs a development roller having an elastic layer is left unattended for a substantial length of time in such a condition that the elastic layer of the development roller remains in contact with the peripheral surface of the photosensitive drum, it is possible for the elastic layer of the development roller to permanently deform. Thus, if an image forming apparatus which employs a development roller having an elastic layer is used after it has been unattended for a substantial length of time, it is possible that the latent image on the photosensitive drum will be nonuniformly developed.
Further, if a development roller remains in contact with a photosensitive drum while no image is formed, it is possible for the developer on the development roller will unnecessarily adhere to the photosensitive drum, regardless of whether the development roller has an elastic layer or not. Further, if the photosensitive drum and development roller are rotated in contact with each other even when the development roller is not used for development, it is possible that the photosensitive drum, development roller, and developer will be prematurely deteriorated by the friction between the photosensitive drum and development roller.
Thus, various proposals have been made to prevent the above described problems. One of the proposals is disclosed in Japanese Laid-open Patent Application No 2007-213024. According to this patent application, the image forming apparatus is provided with a mechanism which acts on each process cartridge so that while no image is formed, the photosensitive drum and development roller in the process cartridge in the apparatus main assembly are kept separated from each other. More specifically, the process cartridges are mounted in the drawer with which the main assembly of the image forming apparatus is provided, so that as the drawing is pushed into the main assembly, the process cartridges are properly positioned for image formation, in the main assembly of the image forming apparatus, and also, so that while the drawer is pushed into, or pulled out of the main assembly, for the installation or removal of the process cartridge, into, or from, the main assembly, the abovementioned mechanism for separating (disengaging) the development roller from the photosensitive drum is kept retracted from the process cartridge installation/removal path, in order to prevent the mechanism from interfering with the process cartridges.